Since the implantation of the first cardiac pacemaker, implantable IMD technology has advanced with the development of sophisticated implantable pulse generators (IPGs), implantable cardioverter-defibrillators (ICDs) arrhythmia control devices designed to detect arrhythmias and deliver appropriate therapies. Detection and discrimination between various arrhythmic episodes in order to trigger the delivery of an appropriate therapy is of considerable interest. Prescription for implantation and programming of the implanted device are based on the analysis of the PQRST electrocardiogram (ECG) and the electro gram (EGM). Waveforms are typically separated for such analysis into the P-wave and R-wave in systems that are designed to detect the depolarization of the atrium and ventricle respectively. Such systems employ detection of the occurrence of the P-wave and R-wave, analysis of the rate, regularity, and onset of variations in the rate of recurrence of the P-wave and R-wave, the morphology of the P-wave and R-wave and the direction of propagation of the depolarization represented by the P-wave and R-wave in the heart. Detection, analysis and storage of such EGM data within implanted medical devices are well known in the art. Acquisition and use of ECG tracing(s), on the other hand, has generally been limited to the use of an external ECG recording machine attached to the patient via surface electrodes of one sort or another.
ECG systems that detect and analyze the PQRST complex depend upon the spatial orientation and number of externally applied electrodes available near or around the heart to detect or sense the cardiac depolarization wave front. Implantable medical device systems increasingly can include communication means between implanted devices and/or an external device, for example, a programming console, monitoring system, and similar systems. For diagnostic purposes, it is desirable that the implanted device communicate information regarding the device's operational status and the patient's condition to the physician or clinician. Implantable devices can transmit or telemeter a digitized electrical signal to display electrical cardiac activity (e.g., an ECG, EGM, or the like) for storage, display and/or analysis by an external device.
To diagnose and measure cardiac events, a cardiologist has several tools from which to choose. Such tools include twelve-lead electrocardiograms, exercise stress electrocardiograms, Holter monitoring, radioisotope imaging, coronary angiography, myocardial biopsy, and blood serum enzyme tests. In spite of these advances in the medical device art, the surface ECG has remained a standard diagnostic tool. A twelve-lead ECG is typically the first procedure used to determine cardiac status prior to implanting a pacing system. An ECG recording device is attached to the patient through ECG leads connected to skin electrodes arrayed on the patient's body so as to achieve a recording that displays the cardiac waveforms in any one of twelve possible vectors. An example of ECG leads with skin electrodes may be seen with respect to U.S. Pat. No. 6,622,046 to Fraley et al. issued Sep. 16, 2003, and assigned to the assignee of the present invention. Fraley et al. discloses a feed through used in combination with an electrode to sense the human body's electrical activity. It is desirable to develop new mechanical features related to securing surface ECG electrodes to the housing of an implantable medical device.